The present invention relates to a rotation controlling device suitable to the servo circuit of a motor used in a video cassette recorder, etc., and more particularly to a motor rotation controlling device which can minimize the transient phenomena of motor in an initial operation and the time to arrive at a normal speed.
A rotation controlling device applied to a drum spindle servo circuit of a video cassette recorder (hereinafter referred to as "VCR") detects a rotation speed of a drum motor from a frequency generator signal generated in a frequency generator (hereinafter referred to as "FG") and yields a speed error of drum motor from the detected rotation speed. And, the rotation controlling device compensates the yielded speed error, and supplies the compensated motor driving signal to a drum motor, thereby keeping the speed of drum motor constant. However, since the rotation controlling device includes rotation defect components, i.e., the drum rotation frequency, 30 Hz, and its harmonic component, generated by the eccentricity of drum, the attachment error of the PF, etc., are included in the yielded speed error, it cannot keep the rotation speed of drum motor constant. And, when the rotation controlling device is initially operated like other rotation controlling devices applied to other fields, the time for arriving at a normal speed, i.e., the transient response time, is long, so that there is a problem in that the video signal is muted for a long time at an initial time of reproduction mode or record mode of VCR.
An improved rotation controlling device to solve the above problem is described in Japanese laid-open Patent No. Sho 63-129877 and No. Pyung 1-117676. The rotation controlling device described in No. Sho 63-129877 removes the unnecessary rotation defect components, i.e., durum rotation frequency, 30 Hz, and its harmonic component, included in the speed error signal yielded by a notch filter in a normal driving mode and drives the drum motor by a motor driving signal compensating the rotation defect component removed speed error signal, thereby keeping the rotation speed of drum motor constant. However, the rotation controlling device described in No. Sho 63-129877 utilizes the notch filter only in a normal driving mode, so that it has the problem of consuming a long time for the rotation speed of drum motor to reach normal speed in an initial operation.
To improve the problem of the rotation controlling device described in No. Sho 63-129877, the rotation controlling device described in No. Pyung 1-117676 varies the transfer function of the notch filter according to the initial operation and the normal speed drive. Thus, in a normal speed drive, even if the gain of a pure speed error component, i.e., "0" Hz component, is decreased, the relatively large rotation defect component is removed, and also in an initial operation, even if the rotation defect component is not completely removed, the gain of zero Hz component increases. However, the rotation controlling device described in No. Pyung 1-117676 can shorten the time for the drum motor speed to reach a normal speed in an initial operation, but there are problems in that the transient phenomena in the motor speed are made more severe by the acceleration of the motor speed and the long time for the drum motor to keep at a normal speed, i.e., a long stabilized time, is consumed. The problems are described with reference to the attached drawings as follows.
With reference to FIG. 1, a conventional rotation controlling device comprising a drum motor 10 and a rotation detector 12 installed in the drum motor 10 is described. The rotation detector 12 comprises an FG head 14 for generating an FG pulse, as shown in FIG. 2A, having a frequency according to a rotation speed of drum motor and a phase generator (hereinafter referred to as "PG") head 16 for generating a PG pulse, as shown in FIG. 2B, according to a rotation phase of the drum motor 10. The PG pulse having one pulse per rotation of drum motor 10 is supplied to a control signal generating circuit 32, and on the other hand, the FG pulse having 6 pulses per rotation of the drum motor 10 is supplied to a control signal generating circuit 18. The first control signal generating circuit 18 resets a counter 20 at the rising edge of the FG pulse as shown in FIG. 2C to start to count, and samples the values N.sub.1, N.sub.2, N.sub.3, . . . counted by the counter 20 at the falling edge of the FG pulse. The sampled count values N.sub.1, N.sub.2, N.sub.3, . . . which are speed error data DS are supplied to a digital notch filter 22 and a control circuit 24. The counter 20 counts up by a clock pulse from a clock generator (not shown) received through an input terminal 48. The control circuit 24 determines an initial operation mode or a normal mode according to a logic value of the speed error data, and varies a transfer function of the comb-shaped filter 22 according to the determined result. Under the control circuit 24, even if the rotation defect component is not removed at an initial driving mode, the comb-shaped filter 22 filters the speed error data DS for the gain of 0 Hz component not to be damped, and at a normal mode, even if the 0 Hz component gain is damped, the speed error data DS is filtered to remove the rotation defect component. A multiplier 26 multiplies the filtered speed error data supplied from the comb-shaped filter 22 by a multiplier coefficient K.sub.1 and supplies the multiplied speed error data to an adder 42. And a differentiator 28 differentiates the filtered speed error data supplied from the comb-shaped filter 22 and generates angular acceleration data. A multiplier 30 multiplies the angular acceleration data generated in the differentiator 28 by a multiplier coefficient K.sub.0 and supplies the multiplied angular acceleration data to the adder 42.
Meanwhile, the second control signal generating circuit 32 resets a counter 34 at the falling edge of the PG pulse supplied from the PG head 16 to start to count. The counter 34 counts up by 1 by a clock pulse supplied through a second input terminal 50 from a clock generator (not shown), samples the counted value at the falling edge of a vertical sync signal such as FIG. 2D supplied through a third input terminal 52 from a sync signal separating circuit (not shown) and supplies the sampled count value as phase error data DP to an integrator 36 and a multiplier 40. The integrator 36 integrates the phase error data DP, and the multiplier 38 multiplies the phase error data integrated in the integrator 36 by a multiplier coefficient K.sub.3 and supplies the integrated and multiplied phase error data to the adder 42. Also, the multiplier 40 multiplies the phase error data DP supplied from the counter 34 by a multiplier coefficient K.sub.2 and supplies the multiplied phase error data to the adder 42. The adder 42 adds the data from the multipliers 26, 30, 38 and 40 and supplies the added data to a digital-analog (hereinafter referred to as "D-A") converter 44. The D-A converter 44 converts the added data supplied from the adder 42 into an analog signal and supplies the converted analog signal to a driving circuit 46 as a speed control signal. The driving circuit 46 controls the speed of the drum motor 10 according to the voltage level of the speed control signal.
FIG. 3 shows a detailed circuit diagram of the D-A converter 44 shown in FIG. 1, and FIGS. 4A and 4B show output waveform diagrams at the respective portions of FIG. 3. In FIG. 3, a timing signal generator 56 generates a pulse width modulated signal having a width corresponding to a logic value of digital data received through an input terminal 54 from the adder 42 shown in FIG. 1. The pulse width modulated signal, a signal having three logic states, as shown in FIG. 4A has a low logic with respect to a high impedance level when the digital data has a plus logic value and to the contrary, has a high logic with respect to a high impedance level when the digital data has a minus logic data. And the pulse period of the pulse width modulated signal has the same period as that of the FG pulse. An operational amplifier 58 constituting an integrator circuit together with a resistor R1 and a capacitor C1 charges/discharges for a pulse width interval according to a logic state of pulse width modulated signal supplied from the timing signal generator 56, thereby generating a speed control signal of analog signal form as shown in FIG. 4B. In more detail, the operational amplifier 58 charges a voltage in a capacitor C1 for a pulse interval when a pulse width modulated signal of low logic state is input, and contrarily, discharges the voltage charged in the capacitor C1 for a pulse interval when a pulse width modulated signal of high logic state is input. The time constant .tau. of charging/discharging of the capacitor C1 is 1/(R.sub.1 C.sub.1) and the voltage charged in the capacitor C1 is supplied to the driving circuit 46 shown in FIG. 1 through an output terminal 60 as a speed control signal So.
FIG. 5 shows speed error data DS outputted from the comb-shaped filter 22 shown in FIG. 1 at an initial operation and a speed control signal So outputted from the D-A converter 44. In FIG. 1, the speed error data DS has a maximum value during the interval T.sub.1, i.e. from the time t.sub.0 to start to drive the drum motor 10 to the time t.sub.1 for the drum motor to reach the first target (or normal) speed, and rapidly decreases to have a minus value during the interval T.sub.2, i.e., from the time t.sub.1 to the time for the drum motor 10 to rotate with a maximum speed, and slowly increases during the interval T.sub.3, i.e., from the time t.sub.2 for the drum motor 10 to have a maximum speed to the time t.sub.3 to be driven with a normal driving mode. Meanwhile, the speed control signal So keeps the output voltage at a maximum according to the speed error data DS during the interval from the time t.sub.0 for the drum motor 10 to be initially operated to the time t.sub.1 for the drum motor 10 to reach a target speed, and rapidly decreases to "0" level during the interval from the time t.sub.1 for the drum motor 10 to reach the target speed to the time t.sub.2 for the drum motor 10 to have a maximum speed. And, the motor speed control signal So keeps "0" level for a constant interval during the interval from the time t.sub.2 for the drum motor 10 to rotate at a maximum speed to the time t.sub.3 to be operated at a normal driving mode.
FIG. 6 shows a rotation speed of the drum motor 10 according to the speed control signal So outputted from the D-A converter 44 shown in FIG. 1, at an initial operation. In FIG. 6, the drum motor 10 is driven and accelerated by a speed control signal of maximum voltage from the driving started time t.sub.0, and reaches the target speed at the time t.sub.1, and then reaches the maximum speed at the time t.sub.2 by rotation inertia even if the speed control signal So is decreased to the "0" level from the maximum value from the time t.sub.1. And the drum motor 10 is rapidly decelerated from the time t.sub.2 and is driven with a normal control mode by a speed control signal So starting to be increased at the time t.sub.3 having below target speed.
As described above, at the initial operation, the conventional rotation controlling device completely detects the error near Hz even if the rotation defect component having a relatively low level is included, and accelerates the motor by the detected error value, so that the transient phenomena are severed and the transient response time until it is driven with a normal driving mode for keeping the target speed constant, lengthens. Moreover, the conventional rotation controlling device utilizing a D-A converter having an integrator for increasing/decreasing by steps the voltage value of the speed control signal by a voltage corresponding to an error amount according to the error amount of motor, has the problem of having more severe transient response characteristic due to a slow response characteristic of the motor speed control signal with respect to the speed variation. Because of these problems, a VCR mutes the video signal for a long time at the initial reproduction and record, thereby inconveniencing the consumer and decreasing the reliability of the VCR.